Effect of the Oxygen Vacancy-Tunable Ce_1–<i>x</i>Gd_<i>x</i>O_2−δ Support on the Ni-Catalyzed CO₂ Utilization via the Reverse Water–Gas Shift Reaction

The reverse water–gas shift (RWGS) reaction offers a critical option for CO2 utilization, yet challenged by the endothermic nature of the reaction and high activation energy required for cleavage of the inert C═O bond. Oxygen vacancy engineering has been increasingly attractive as an effective strategy to activate CO2 via the electrostatic interaction. Herein, we develop a novel RWGS catalyst by dispersing metallic nickel on the gadolinia-doped ceria (GDC) support, where the oxygen vacancy concentration is tuned by varying the Gd/Ce molar ratio. The electron paramagnetic resonance (EPR), Raman, and X-ray photoelectron spectrometry (XPS) characterization of the Ni-GDC catalysts revealed that the oxygen vacancy concentration of the catalysts was increased with the increasing doping percent of Gd until 50%, and the interaction between metallic Ni and the GDC support kept strengthening as the Gd percent was increased. The developed Ni-GDC catalysts exhibited excellent activity and stability in driving the RWGS reaction, achieving a maximum CO yield of 19.4 mmol g–1 min–1 at 700 °C and retaining stable catalytic performance with no loss of activity throughout 20 h of the continuous test. It was found in this study that the CO2 conversion rate of the catalyst was positively correlated with its oxygen vacancy concentration, despite the observation that the oxygen vacancy concentration was less influential to CO2 conversion compared to temperature and the H2/CO2 feeding ratio.